Addon subdomains and subdomains

Hi, it was discussed here, but it hasnt changed since then.
Cpanel has two types for virtual servers - addon domains and subdomains.
At first glance, they seem independent. But when you create addon domain, automatically Cpanel creates subdomain thus decreasing the total number of subdomains. Also it creates some ftp users, directories and so on.

Apparently they do. I don't recall the reason for this, but it's probably been mentioned in a thread on the topic in the past. If you want a definitive answer you'll probably have to contact cPanel directly.